It is well known to dope molybdenum material with various substances. For example, doping with potassium and silicon in the form of a potassium silicate solution, has been proposed, see for example the referenced U.S. Pat. No. 4,419,602, Mitamura et al, which describes use of K and Si as additives to molybdenum for molydenum sealing foils. It is intended to, thereby, increase the re-crystallization temperature. It has been found that the characteristics of the materials of the doped molybdenum exhibit a substantial spread so that it was difficult to provide a material with precisely defined characteristics. It could be obtained only by mixing of various components in a very difficult working step, to be carried out after the material has been first prepared.
It has also been proposed to dope molybdenum material with iron and/or cobalt, see for example East German (GDR) Patent 49 592, Uhlmann. A higher breaking strain was intended to be obtained by so doping the molybdenum. In the meanwhile, however, it has been found that cobalt is a highly toxic substance requiring tight hygienic control in the workplace to protect workers handling the material. The desired and intended characteristics with respect to elongation and strength also could not be precisely predicted, since the spread of characteristics was large; manufacture, thus, resulted in substantial amounts of scrap and reject material.
The requirements placed on thermal and mechanical loading of molybdenum material have recently continuously increased, particularly in connection with the development of halogen incandescent lamps and PAR lamps. This requirement led, first, to increased specialization of the molybdenum material for specific and distinct uses. For example, different molybdenum materials were made and provided depending on the use, for example for core wires, gas-tight melt-in pins or wires, holding wires, and sealing foils, respectively. Holding or support wires must have, as the most important characteristic, high and constant elongation; sealing foils, on the other hand, must have, primarily, high ductility and high recrystallization temperature. Holding wires are used to support incandescent coiled filaments, secured at their ends--see for example the referenced U.S. Pat. No. 4,138,623, McMillan. The wires, further, must have high strength, that is, resistance with respect to breakage, and high re-crystallization temperature. Pins or wire elements which are to be melted into glass, and core wires, require an appropriate combination of high re-crystallization temperature and high flexing or bending number.
These are their most important characteristics. In pins or wire elements intended to be melted into glass, it is also important that they are free from fissures, splits and crevasses.
The various and specific requirements of these molybdenum materials can be--to some degree--obtained or controlled by respectively different constitution of the material, and/or respectively selected doping with potassium and/or, if desired, possibly also by silicon. This, however, renders machinery to make the molybdenum material extremely complex and expensive. It required new set-ups for manufacturing machinery each time a different molybdenum material was to be made, new programming thereof, and hence was costly. Since one cannot tell, merely by outside appearance what the specific constituents of any molybdenum material are, the danger of mistakes was ever present.
The problem of wide spread of characteristics was, heretofore, not solved. Continuous re-adjustment of production machinery was necessary to prevent manufacture of excessive amounts of scrap material. This was particularly so when adding the respective doping materials. The disagreeable choice presented itself, either to accept a substantial manufacture of scrap material or to use material which met the required characteristics only marginally. For example, if the material is subject to splitting or fissuring, the risk that the halogen cycle within a lamp is thereby affected by contaminants had to be accepted. Such contaminants, however, led to rapid destruction of the lamp and substantially decreased lifetimes with respect to design levels.